akka.stream.stage

Class DetachedStage<In,Out>

java.lang.Object

akka.stream.stage.AbstractStage<In,Out,UpstreamDirective,DownstreamDirective,DetachedContext<Out>,LifecycleContext>

akka.stream.stage.DetachedStage<In,Out>

All Implemented Interfaces:

Stage<In,Out>

Deprecated.

Please use GraphStage instead. Since 2.4.2.

public abstract class DetachedStage<In,Out>
extends AbstractStage<In,Out,UpstreamDirective,DownstreamDirective,DetachedContext<Out>,LifecycleContext>

DetachedStage can be used to implement operations similar to buffer, expand and conflate.

DetachedStage implementations are boundaries between 1-bounded regions. This means that they need to enforce the "exactly one" property both on their upstream and downstream regions. As a consequence a DetachedStage can never answer an AbstractStage.onPull(Ctx) with a Context.pull() or answer an AbstractStage.onPush(In, Ctx) with a Context.push(Out) since such an action would "steal" the event from one region (resulting in zero signals) and would inject it to the other region (resulting in two signals).

However, DetachedStages have the ability to call akka.stream.stage.DetachedContext#hold as a response to AbstractStage.onPush(In, Ctx) and AbstractStage.onPull(Ctx) which temporarily takes the signal off and stops execution, at the same time putting the stage in an akka.stream.stage.DetachedContext#isHolding state. If the stage is in a holding state it contains one absorbed signal, therefore in this state the only possible command to call is DetachedContext.pushAndPull(Out) which results in two events making the balance right again: 1 hold + 1 external event = 2 external event

This mechanism allows synchronization between the upstream and downstream regions which otherwise can progress independently.

See Also:

PushPullStage

Nested Class Summary

Nested classes/interfaces inherited from class akka.stream.stage.AbstractStage

AbstractStage.PushPullGraphStage<In,Out,Ext>, AbstractStage.PushPullGraphStageWithMaterializedValue<In,Out,Ext,Mat>

Constructor Summary

Constructors

Constructor and Description
DetachedStage() Deprecated.

Method Summary

Modifier and Type	Method and Description
Supervision.Directive	decide(java.lang.Throwable t) Deprecated. If an exception is thrown from AbstractStage.onPush(In, Ctx) this method is invoked to decide how to handle the exception.
boolean	isDetached() Deprecated. INTERNAL API

Methods inherited from class akka.stream.stage.AbstractStage

onDownstreamFinish, onPull, onPush, onUpstreamFailure, onUpstreamFinish, postStop, preStart, restart

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DetachedStage

public DetachedStage()

Deprecated.

Method Detail

isDetached

public boolean isDetached()

Deprecated.

Description copied from class: AbstractStage

INTERNAL API

Overrides:

isDetached in class AbstractStage<In,Out,UpstreamDirective,DownstreamDirective,DetachedContext<Out>,LifecycleContext>

Returns:

(undocumented)

decide

public Supervision.Directive decide(java.lang.Throwable t)

Deprecated.

If an exception is thrown from AbstractStage.onPush(In, Ctx) this method is invoked to decide how to handle the exception. By default this method returns Supervision.Stop.

If an exception is thrown from AbstractStage.onPull(Ctx) or if the stage is holding state the stream will always be completed with failure, because it is not always possible to recover from that state. In concrete stages it is of course possible to use ordinary try-catch-recover inside onPull when it is know how to recover from such exceptions.

Overrides:

decide in class AbstractStage<In,Out,UpstreamDirective,DownstreamDirective,DetachedContext<Out>,LifecycleContext>

Parameters:

t - (undocumented)

Returns:

(undocumented)